Electrolytic cell for the production of aluminum



Dec. 15, 1964 .1. HENRY ETAL 3,161,579

ELECTROLYTIC CELL FOR THE PRODUCTION OF ALUMINUM Filed March 6, 1961 2Sheets-Sheet 1 FUSED SALT l5 MOLTEN ALUM|NUN:4

MOLTEN l3 M ZELREFRACTORY HARD METAL IN VEN TORS JACK L. HENRY BYWILLIAM A. KLEMM 9 1964 i J. HENRY ETAL 3,

ELECTROLYTIC CELL FOR THE PRODUCTION OF ALUMINUM Filed March 6, 1961 2Sheets-Sheet 2 D.C. 2 (I A i E 11 35 o.c.+ 0.c.+ [34 Q L; i

L E 34 D.C.+ o,c.+ (I 4 E I E- 3 :E Il3- 4:

INVENTORS JACK L. HENRY BY WILLIAM A. KLEMM United States Patent3,161,579 ELECTRQLYTHQ CELL lFtOR THE PRGDUQJ'EEQ N 63F ALUlt HNUM.laclr L. Henry, Los Altos, and William A. Klernm, Morita Vista, Calif.,assignors to Kaiser-Aluminum tlhernh call Corporation, Galdanti, Qaliii,a corporation of Delaware Filed Mar. 6, 1961, Ser. No. 93,539

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This invention relates in general to electrolytic cells for theproduction of aluminum. More particularly, the

invention relates to a new and improved electrolytic aluminum reductioncell design utilizing refractory hard metal current-conducting bodies.

As used herein in the specification and the claims the expressionrefractory hard metals refers to materials which possess a lowelectrical resistivity, a low solubility in molten aluminum and moltenelectrolyte under cell operating conditions, are wettable by moltenaluminum under cell operating conditions, and have good stability underconditions existing at the cathode of a reduction cell. The preferredrefractory hard metal material for at least that portion of the surfaceof such element in contact with the molten aluminum consists essentiallyof at least one of the materials selected from the group consisting ofthe carbides and borides of titanium, zirconium, tantalum and niobium,and mixtures thereof. Such materials being found to exhibit all orsubstantially all of the above properties.

The expression consisting essentially as used here inafter in thespecification and the claims means that the refractory hard metalmaterial referred to above does not contain other substances in amountssufficient to materially aifect the desired characteristics of thematerial, al-

though other substances may be present in minor amounts which do notmaterially affect such desirable characteristics, for example, smallproportions of oxygen, nitrogen, titanium, nitride, and iron in therefractory hard metal subtance.

Conventionally, carbon cathodes as well as carbon ano'des have been usedin the electrolytic reduction cells for the production of aluminium.Cathodes made of carbon possess a number of disadvantages particularlyirl'regard to their use in electrolytic reduction cells for theproduction of aluminum. Carbon cathodic elements are subject topenetration by fused bath electrolyte and molten metal and exhibitundesirable swelling. In addition carbon cathodes are not wetted bymolten aluminum under'cell operating conditions and have relatively highelectrical resistance. Furthermore, the cathode should be rugged andpossess the necessary strength to permit its handling and use withoutexcessive cracking, breaking or chipping. The use of carbon cathodes,therefore, has contributed significantly to the cost of aluminiumproduction.

ments are:

(1) Horizontal side entering wherein the refractory gdblfilb PatentedDec. 15, 1964 hard metal elements extend horizontally through thevertical side walls of the reduction cell and-project at their interiorextremities into the molten aluminum layer;

(2) Top entering refractory hard metal elements wherein the elementsare'disposed along the sides of the cavity or chamber of the cell andenter into the cell at the solidified crust and molten electrolyte andterminate at their extremities a short distance above the base of theing the elements constitute one significant problem encountered whenusing refractory hard metal elements. The furnace design should be suchthat'the refractory hardmetal elements are subjected to the minimumamount of mechanical stress caused by distortions in the furnace liningstructure and in furnace operation. Furthermore, such elements which areto be subjected to the abuse in mechanical handling and stress imposedof the magnitude found in electrolytic reduction cell operation, arerelatively difficult to fabricate.

Another problem with refractory hard metal elements used as suggested bythe above mentioned French patent is the necessity of maintainingthecathod-ic elements and the cathode metal layer'in direct contact witheach other. If the heat generation in'a particular section of the cellcavity is reduced below normal, a ledge of frozen electrolyte may growon the walls and bottom of the cavity around that section, and thisledge may envelop and cover any elements near :it, thereby breakingcontact between the elements and the metal layer. To prevent theinterruption of contact between the elements and the metal it isnecessary to prevent the muck (a loose mixture of undissolved aluminaand frozen electrolyte which sinks through the cathode metal layer) frombuilding up under the cathode metal layer and disrupting the cathodesurface thereby interferring with the necessary flow of current. Themuck build-up is prevented by periodically raking and redispersing themuck so formed. Cell design involving horizontal side entering elementsas in (1) above have exhibited difiiculties with muck under the cathodemetal layer and with excessive ledging of frozen bath enveloping thecathode elements. Further, relatively long pieces of refractory hardmetal material are required in all three above arrangements (horizontalside entering, top entering and bottom entering elements) because of thethick insulation and cell lining of the side and bottom necessary inconventional reduction furnaces V to contain the molten cryolite bathand aluminum through which the elements must pass. In cells with topentering cathodic elements along the side walls of the cell (2 above),the elements may interfere with normal cell operation particularly withbreaking in of the crust at the sides of the cavity. Further,insertion'of the bars through the crust entails additional risk ofbreakage of to a minimum amount of mechanical stress.

the refractory hard metal cathodic elements which would therebynecessitate replacement of the cathodic elements. In cells with bottomentering cathodic elements (3 above), the elements are very susceptibleto damage during raking. In addition to the above-mentioned disadvantageof undue lengths required to penetrate the cell insulation and lining,it should also be noted that the fabrication of refractory hard metalelements in the lengths required for top entering, horizontal sideentering and bottom entering designs as discussed above, is relativelydifficult and very expensive.

Because these refractory hard metals are inherently expensive, one ofthe major problems in designing reduction cells employing refractoryhard metal current-conducting elements is that of being able to utilizea minimum possible amount of the refractory hard metal material andstill accomplish the maximum advantages of using these materials ascathodic elements. In addition, the inherent fragility of theserefractory hard metal materials poses a problem in furnace design. Thedesign of furnaces should be such that refractory hard metal elementsare subjected The susceptibility of refractory hard metal to oxidationand corrosion by electrolyte imposes further restriction on furnacedesign to provide a minimum oxidation of the elements. The refractoryhard metal current-conducting elements should also be removed from thework area where mechanical abuse is unavoidable.

All of the above disadvantages accompanying the use of refractory hardmetal elements may be avoided while still securing the greatly improvedelectrolytic cell operation resulting from the use of refractory hardmetal current-conducting elements by this novel cell design. Accordingto the invention there is provided an electrolytic cell for theproduction of aluminum having side Walls and a bottom floor, at leastone refractory wall structure dividing said cell into at least onecathode current collecting chamber and at least one electrolyticreduction chamber, said electrolytic reduction chamber adapted tocontain a molten aluminum layer in the lower portion thereof and a bodyof fused salt electrolyte above said molten aluminum layer and incontact therewith, an anode member disposed at least partially in saidelectrolytic reduction chamber and in contact with the fused saltelectrolyte, molten aluminum at least partially filling said cathodecurrent collecting chamber and maintained out of physical contact withthe molten aluminum and fused salt electrolyte in said electrolyticreduction chamber by said refractory wall structure, a cathode member atleast partially disposed in said cathode current collecting chamber andin contact with the molten aluminum contained therein, said refractorywall structure comprising substantially nonelectrically conductiverefractory material and including current conducting refractory hardmetal bodies disposed at the lower portion thereof in such a manner asto provide an electrical path between the molten aluminum in theelectrolytic reduction chamber and the molten aluminum in the cathodecurrent collecting chamber.

Various objects and advantages of the instant invention will be apparentfrom the ensuing description thereof.

The invention generally comprises an electrolytic cell having at leasttwo chambers or compartments, at least one cathode current collectingchamber and at least one electrolytic reduction chamber. A refractorydividing wall structure, which may be constructed primarily of asuitable refractory brick, separates the current collecting chamber fromthe reduction chamber. The cathode current collecting chamber containsmolten aluminum metal or alloy which is kept entirely free of theelectrolyte bath by the dividing wall and becomes a current collectingwell. At least one refractory hard metal body in the form of a brick ora half brick is incorporated in the refractory dividing wall. Cathodiccurrent leads, which may also be of refractory hard metal, areelectrically connected to tr e cathode bus and are inserted and immersedinto the molten aluminum metal in the current collecting well.

l Thus, the metal in the well is electrically connected, withoutphysical contact, to the metal bath in the main portion of theelectrolytic reduction cell through the refractory hard metal bricks inthe refractory dividing wall.

This combination makes possible the use of short lengths of refractoryhard metal material for the current conducting bodies in the refractorywall. In addition, the cathodic current leads contacting the moltenaluminum in the Well are maintained out of the portion of theelectrolytic cell where they would be exposed to relatively hightemperatures. Suitable connections with aluminum, or other metal, capsand cathode bus connecting means can be made in lower temperatureregions where conditions are less severe thereby further minimizingstructural failures and chance of cell stoppage. The metal in the wellis maintained at a considerably lower temperature than the cell, i.e.,660950 (1., thus further serving to reduce the rate of corrosion ofrefractory hard metal current leads. The refractory hard metal bricks orhalf bricks incorporated into the refractory dividing wall are extremelyrugged and far less subject to thermal shock and mechanical abuse byvirtue of the more compact form.

The problem of muck and ledge is readily eliminated in the cell designof the instant invention due to the easy accessibility of the refractoryhard metal brick surfaces to mechanical tools. Muck and/ or ledge couldbe removed mechanically with bars, rakes or specially designed toolswithout fear of damage to the refractory hard metal body. Furthermore,the refractory hard metal bricks or half bricks can be incorporated intothe dividing wall in accordance with optimum thermal design to insurelocalization of heat generation. The cooler metal in the well free ofthe electrolyte bath provides an excellent collector from which thecurrent is removed to the cathode bus.

In the accompanying drawings are illustrated one preferred embodiment ofthe instant invention as applied to aluminum reduction cells.

In the drawings:

FIG. 1 is a fragmentary longitudinal vertical view partly in section ofone embodiment of an electrolytic cell which is suitable for carryingout the invention and showing the position of the refractory wallstructure with respect to the cathode current collecting chamber andelectrolytic reduction chamber;

FIG. 2 is a front elevational view of the refractory wall structureshown in FIGURE 1 and depicts the disposition of the refractroy hardmetal bodies within the wall.

FIG. 3 is a fragmentary plan View of the cell of FIG- URE l and showsthe disposition of the refractory wall and current collecting wellwithin the illustrated cell.

FIG. 4 is a fragmentary plan view of an electrolytic cell illustratinganother embodiment of the invention wherein the refractory Wallstructure containing the refractory hard metal current conducting bodiesis in the form of a shell-like structure.

FIG. 1 which is a fragmentary longitudinal vertical view partly insection of an elongated aluminum reduction cell suitable for practice ofthe invention shows an electrolytic reduction cell 10, generallycomprising a metal shell 11, e.g., of steel, within which is disposed aninsulating lining 12, which can be of any desired insulating materialsuch as alumina, bauxite, clay or aluminum silicate brick. Within theinsulation 12 is disposed refractory cell lining 13, which can be of anydesired material for example, carbon, alumina, fused alumina, siliconcarbide, silicon nitride, bonded silicon carbide or other desiredmaterials. Most commonly, the lining is made up of a plurality of carbonblocks or is a rammed carbon mixture or a combination of a rammed carbonmixture for the bottom or floor of the lining with side and end wallsconstructed of blocks of carbon. Alternatively, the side and end wallscan be constructed of silicon carbide bricks or other suitable material.The lining 13 defines a cavity or chamber Within which is disposed apool or layer of molten aluminum 14. The molten aluminum layer 14 isnormally rebricks or half bricks 22.

ferred to as a metal pad. Also disposed within the chamber and incontact with the aluminum layer 14 is a body or layer 15 of moltenelectrolyte, e.g., cryolite. The molten electrolyte bath 15 is coveredby solid crust layer 16 which consists essentially of frozen electrolyteconstituents and additional alumina. As alumina is consumed inelectrolyte 15 the frozen crust is broken and more alumina is fed intothe electrolyte. Disposedat least partially within the chamber andpartially immersed in electrolyte layer 15 are prebaked carbon anodes17. Although prebaked carbon anodes are shown in the embodiment, eitherprebaked or the self-baking anodes known in the art may be employed inthe invention. Anode i7 is connected by suitable means, not shown, tothe positive pole of a source of electrolyzing current. Ledge Zli whichis an extension .of crust 16 consists of frozen electrolyte constituentsand provides protection to the refractory wall structure 21,

which may be of any suitable refractory brick, from attack of 'moltenaluminum and molten electrolyte.

.Within refractory dividing wall 21 are disposed a limited number ofrefractory hard metal bodies in the form of in the embodiment shown inFIGURES l and 3, dividing wall 21 is spaced from a side- .Wall 3.0 insuch a manner as, to provide a well I'll. Molten aluminum, or alloy, atleast partially fills the well 31 and refractoryhardmetal current leads32 are at least partially immersed in the molten aluminum bath in wellill. Re-

fractory hardmetal current leads 32 are capped with a suitable cappingmetal 33, e.g., aluminum, which serves to connect the refractory hardmetal current lead to a flexible connecting means 34, forming cappedcurrent lead assembly 40, which is electrically connected to the cathode.bus 35. When thus assembled the anode i7 is electrically connected tothe cathode bus through the electrolyte 15, the metal bath i4,refractory hard metal bodies 22 in the dividing wall, current collectorbath 31, refractory hard metal current lead 32, capping 33, and flexiblecon necting means 34. Hence, the metal in thewell and the metal pad areelectrically connected without being in physical contact.

FIG. 2 is a front elevational view of the refractory wall structure 21composed primarily of refractory bricks 23 and incorporating a limitednumber of refractory hard 'A number of capped current lead assembliesare depicted withinthe current collecting chamber 24, however,

any suitable number of leads may be employed. Flex connecting means 34are shown electrically connecting capped current lead assemblies 4d tocathode bus 35.

FIG. 4 depicts an embodiment wherein the refractory wall is a shell-likestructure having three sides and forming with a portion of a side wallof the cell ill, a

current collecting chamber 24 which is separated from reduction chamber25. Flex connecting means 34 electrically connect cappedcurrent leadassemblies 4% to cath- 'ode bus 35.

The current lead 32, which may also be of refractory hard rrietalmaterial, may be joined to an aluminum cond'uctor member 33 tofacilitate the attachment of a flexible connecting means enabling therefractory hard metal element 32 to be electrically connected to thecathode bus "35. This procedure is referred to as capping the refractoryhard metal element. The elements maybe capped in any convenient manner;one satisfactory method being disclosed in the copending application oflack L. Henry, SN. 729,621, filed April 21, 1958, now US. Patent No.

. 3,100,338. This method generally comprises a cleaning of therefractory hard metal member at the portion of the surface where thejoint is to be made, preheating the refractory hard metal member to atemperature above the melting point of aluminum, contacting therefractory hard metal member While at said preheating temperature with amolten flux consisting essentially of the fluorides of sodium, aluminumand lithium, and sodium chloride, and then contacting the refactory hardmetal member with molten aluminum after which the refractory hard metalmember and the aluminum are allowed to cool. The joint which is formedbetween the refractory hard metal member and the aluminum has superiormechanical strength and electrical conductivity characteristics.Flexible connecting means 34 are preferably comprised of multiple leavesof aluminum. One method of connecting the flex to a refractory hardmetal element isby welding the end of the flex to the metal cap whichhas been cast on to the end of the bar, another method is to set one endof the flex which has beenheated into the molten aluminum during thecapping'operation, theconnection is then allowed to cool in the samemanner.

I A number of significant advantages are achieved by the inventive celldesign above described. Bylplacing the refractory hard metal b'odieswithin the dividing wall the use of elements protruding into theelectrolytic cellis avoided. The problem of growth of muck depositsunder the cathode is substantially reduced since all sides of the cellsare free of protruding refractory hard metal elements and are thereforeopen to efficient raking.

In the embodiment illustrated in FIG. 1 the alumina may be fed to thecells in the conve ntional manner by breaking crust anywhere in the cellbut without the danger' of breakage of protruding refractory hard metalelements. The employment of a current-collecting well refractory hardmetal material which can be used in this novel cell design arecharacterized by relatively simple a fabrication methods which yieldsuperior current conducting elements. Prior cell designs utilizedrefractory hard metal elements of large configurations and considerablelengths. In contrast to this, the refractory hard metal elements used inthis invention are relatively short bodies which lend themselves toeasier fabrication by hot pressing or cold forming followed bysintering. If desired after initial fabrication, the bodies couldadditionally undergo a form of heat treatment to relieve stresses, f orexample, a post sintering operation within the same sintering furcordingto the invention permits the use of refractory hard metal elementscapable of production by fabrication techniques which offer significanteconomic advantages over the manufacture of longer bodies and result invery rugged shapes. i M

Although the embodiment depicted in FIG. 1 and discussed above, involvesthe use of one well and one refractory wall structure, it should beexpressly understood that electrolytic cells according to this inventioncan employ a plurality of current-collecting wells and refractorydividing walls depending upon the size and intended capacity of theelectrolytic reduction cell. Further, While the cathode currentcollecting chamber has beendescribed in PEG. 1 as being connected acrosstwo opposite side walls, the cathode may be located anywhere in theelectrolytic cell as, for example, a shell-like structure wherein therefractory wall is three-sided and attached to a portion of the sidewall which serves as the fourth side of the It is apparent, therefore,that the cell design acti current collecting well so formed (FIG. 4).Moreover, the refractory wall structure may extend across to any twoside walls.

In the event the cathode is disposed away from a side wall, a refractorywall structure of any suitable configuration, such as a tube orcylinder, may be employed to isolate the cathode current collectingchamber from the electrolytic reduction chamber thus forming a currentcollecting well containing molten aluminum which facilitates theelectrical connection from the anode through the refractory hard metalcurrent conducting bodies in the refractory wall structure as describedabove. It is clear, therefore, that the invention is not limited to theillustrative embodiment presented and that various changes may be madewithout departing from the spirit and scope thereof, the invention beinglimited only as defined in the following claims wherein, what is claimedis:

1. In an electrolytic cell for the production of aluminum having sidewalls and a bottom floor, at least one refractory wall structuredividing said cell into at least one electrolytic reduction chamber andat least one cathode current collecting chamber, said refractory wallstructure comprising substantially non-electrically conductiverefractory material and including at least one current conductingrefractory hard metal body disposed in the wall and adapted to passelectric current from an anode in the electrolytic reduction chamber toa current lead in the cathode current collecting chamber.

2. An electrolytic cell as in claim 1 wherein the current lead in thecathode current collecting chamber is comprised of refractory hard metalmaterial.

3. An electrolytic cell for the production of aluminum having side wallsand a bottom floor, at least one refractory wall structure dividing saidcell into at least one reduction chamber and at least one currentcollecting chamber, said reduction chamber adapted to contain a moltenaluminum layer confined in said reduction chamber in the lower portionthereof and a body of fused salt electrolyte above said molten aluminumlayer and in contact therewith, said refractory wall structurecomprising substantially non-electrically conductive refractory materialand including current conducting refractory hard metal bodies adapted topass electric current from an anode in the electrolytic reductionchamber to a current lead in the cathode current collecting chamber.

4. An electrolytic cell for the production of aluminum havingside wallsand a bottom floor, said cell having at least one shell-like refractorywall structure dividing said cell into at least one electrolyticreduction chamber and at least one cathode current collecting chamber,said shell-like refractory wall structure being on contact with at leasta portion of a side wall and the bottom floor and open at the upper end,said shell-like refractory Wall structure comprising substantiallynon-electrically conductive refractory material and including current:conducting refractory hard metal bodies adapted to pass electriccurrent from an anode in the electrolytic reduction chamber to a currentlead in the cathode current collecting chamber.

5. An electrolytic cell as in claim 4 wherein the current lead in thecathode current collecting chamber is comprised of refractory hard metalmaterial.

6. An electrolytic reduction cell for the production of aluminum havingside walls and a bottom fioor, at least one refractory wall meansdividing said cell into at least one electrolytic reduction chamber andat least one cathode current collecting chamber, said reduction chamberadapted to contain a molten aluminum layer in the lower portion thereofand a body of fused salt electrolyte above said molten aluminum layerand in contact therewith, said cathode current collecting chambercontaining a body of molten aluminum separate and apart from said lastmentioned molten aluminum layer, the molten aluminum in said cathodecurrent collecting chamber being maintained out of physical contact withsaid molten aluminum and fused electrolyte in said reduction chamber bysaid refractory wall means, said refractory wall means comprisingsubstantially non-electrically conductive refractory material and atleast one current-conducting refractory hard metal body adapted toprovide an electrical path between the molten aluminum in the reductionchamber and the molten aluminum in the cathode current collectingchamber.

7. An electrolytic cell for the production of aluminum having side wallsand a bottom floor, at least one shelllilie refractory wall structuredividing said cell into at least one reduction chamber and at least onecathode current collecting chamber, said cathode current collectingchamber being defined by said shell-like structure in contact with atleast a portion of a side wall and bottom floor, said reduction chamberadapted to contain a molten aluminum layer in the lower portion thereofand a body of fused salt electrolyte above said molten aluminum layerand in contact therewith, molten aluminum separate and apart from saidlast mentioned molten aluminum layer at least partially filling saidcathode chamber and maintained out of physical contact with said moltenaluminum and electrolyte in the anode chamher by said shell-likerefractory wall structure, said shelllike refractory wall structurecomprising substantially non-electrically conductive refractory materialand current-conducting refractory hard metal bodies adapted to providean electrical path between the molten aluminum in the reduction chamberand molten aluminum in the cathode current-collecting chamber.

8. An electrolytic cell for the production of aluminum having side wallsand a bottom floor, at least one refractory wall structure dividing saidcell into at least one cathode current collecting chamber and at leastone reduction chamber, said reduction chamber adapted to contain amolten aluminum layer in the lower portion thereof and a body of fusedsalt electrolyte above said molten aluminum layer and in contacttherewith, at least one anode member disposed at least partially in saidreduction chamber and in contact with the fused salt electrolyte, moltenaluminum separate and apart from said last mentioled molten aluminumlayer at least partially filling said cathode current collecting chamberand maintained out of physical contact with the molten aluminum andfused salt electrolyte in said reduction chamber by said refractory wallstructure, a current lead at least partially disposed in said cathodecurrent collecting chamber and in contact with the molten aluminumcontained therein, said refractory Wall structure comprisingsubstantially non-electrically conductive refractory material andincluding current-conducting refractory hard metal bodies disposed atthe lower portion thereof in such a manner as to provide an electricalpath between the molten aluminum in the reduction chamber and the moltenaluminum in the cathode current-collecting chamher.

9. An electrolytic cell as in claim 8 wherein the current lead in thecathode current collecting chamber comprises refractory hard metalmaterial.

10. An electrolytic cell for the production of aluminum having sideWalls and a bottom floor, at least one shell-like refractory wallstructure dividing said cell into at least one cathode currentcollecting chamber and at least one reduction chamber, said cathodecurrent collecting chamber being defined by said shell-like refractorywall structure in contact with at least a portion of a side wall andbottom floor, said reduction chamber adapted to contain a moltenaluminum layer in the lower portion thereof and a body of fused saltelectrolyte above said molten aluminum layer in contact therewith,molten aluminum separate and apart from said last mentioned moltenaluminum layer at least partially filling said cathode currentcollecting chamber and maintained out of physical contact with themolten material in said reduc- 9 tion chamber by said shell-likerefractory wall structure, at least one anode member disposed at leastpartially said reduction chamber and in contact with said fused saltelectrolyte, at least one current lead disposed at least partially insaid cathode current-collecting chamber and in contact with said moltenaluminum contained therein, said shell-like refractory wall structurecomprising substantially non-electrically conductive refractory materialand current conducting refractory hard metal bodies disposed in the wallin such a manner as to provide an electrical path between the moltenaluminum in the reduction chamber and the molten aluminum in the cathodecurrent-collecting chamber.

References Cited in the file of this patent UNITED STATES PATENTS1,741,469 Long Dec. 31, 1929 2,512,206 Holden et a1. June 20, 19502,915,442 Lewis Dec. 1, 1959 FOREIGN PATENTS 201,350 Switzerland Nov.30, 1938 257,787 Switzerland Apr. 16, 1949

1. IN AN ELECTROLYTIC CELL FOR THE PRODUCTION OF ALUMINUM HAVING SIDEWALLS AND A BOTTOM FLOOR, AT LEAST ONE REFRACTORY WALL STURCTUREDIVIDING SAID CELL INTO AT LEAST ONE ELECTROLYTIC REDUCTION CHAMBER ANDAT LEAST ONE CATHODE CURRENT COLLECTING CHAMBER, SAID REFRACTORY WALLSTRUCTURE COMPRISING SUBSTANTIALLY NON-ELECTRICALLY CONDUCTIVEREFRACTORY MATERIAL AND INCLUDING AT LEAST ONE CURRENT CONDUCTINGREFRACTORY HARD METAL BODY DISPOSED IN THE WALL AND ADAPTED TO PASSELECTRIC CURRENT FROM AN ANODE IN THE ELECTROLYTIC REDUCTION CHAMBER TOA CURRENT LEAD IN THE CATHODE CURRENT COLLECTING CHAMBER.